2006 Renault Master Oil Pressure Switch Fault?

I run a low mileage Renault Master 3.0 dCi based motorhome. I bought it 18 months ago with 13k miles on the clock, and have added around 5k miles in that time; it runs perfectly. However, in all that time sometimes - and it only seems to happen when the engine is hot (but is still only intermittent) - when I start the engine I get an 'Oil Warning' flashing for about a minute, and the 'Service' light stays on. No other symptoms, temp remains normal, and oil is in good condition with no loss. If the engine starts 'normally' ie without the warnings, they do not come on when the engine is running.

I suspect the oil pressure sensor is faulty - can anyone confirm this looks the likely culprit, and if so, where is it located, and how easy is it to replace....?

The problem is not causing me a problem, but I worry that one day the warnings will actually mean something, and I'll ignore them....